Various substances are packaged in a dissolvable or liquid permeable package so that the package can be immersed in a liquid to dissolve or infuse the contents of the package into the liquid. E.g., shredded tea leaves are commonly packaged in a mesh bag so that water can permeate the bag and elute the tea from the leaves. Some clothes washing detergents are packaged in a dissolvable package so that, when the package is placed in a washing machine, the package will dissolve and the detergent will dissolve in the washing water.
Experience shows that infusion of the contents of a package placed in an extracting liquid occurs more quickly and completely if the package does not lie at the bottom of the liquid container, but moves in the upper layers of the liquid. With tea bags, this can be attributed to the following: (1) the upper layers of water have higher temperatures than the layers near the bottom, (2) the part of the package, which usually contacts the bottom, now contacts only water and hence is fully involved in the infusion process, (3) water layers surrounding the package are more actively stirred. That is why most tea bag users commonly agitate the bags' strings during infusion.
Numerous attempts have been made to accelerate the rate of infusion. The following is a list of some patents in this area: